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Author Topic: Z Axis loosing steps in the up direction only.  (Read 6859 times)

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Z Axis loosing steps in the up direction only.
« on: January 23, 2014, 08:51:49 PM »
As the title states, my trusty router has developed a problem with it's Z axis motor loosing steps in the ^UP^ direction only.
This started after I gave mach3 a command to GOTOZ whilst doing some rotary carving on my 4th axis. It was a very stupid command to give, as that drove the cutter all the way into the job and ruined it. ::) I have the Z zero alinged with the center of my part and I've only just started experimenting with the 4th axis. Lesson learnt. :-[

Seeing that my project was ruined, I decided to complete the run and confirm that the job was going to turn out as I'd liked. This is when all my dramas started.
While running the rest of the code the Z axis started making strange noises and proceeded to drive deeper into the job.

I decided that I must have damaged the axis somehow, so I pulled it apart expecting to find a rough bearing or ball screw, but everything looked fine. I then ran the stepper without it being connected to the ball screw and found that jogging in the down direction the motor runs perfectly, but jogging in the up direction the motor jerks and moans and looses steps. Sometimes it even runs the wrong direction. The DRO appears to cycle as per normal and the soft limits were still working as they should.

I have changed motors and driver boards around and the problem still exists only in the Z axis UP direction. I have checked all my motor tuning settings and every other setting that I can think of and they are all set as they have been for years. So nothing has changed in the program that I can see.

My machine is running Probotix BOB and stepper drives, as well as their motors and power supply.
I've been running X Y & Z on 1/4 steps without a problem, and the rotary axis is running 1/8th stepping.
Could I have a bad BOB or parallel port pin? I have had the computer mother board go bad before and that made me suspect the BOB, but with some help from Probotix I was able to diagnose that the mother board had failed. The current board has been running fine for the last year or so.

Could anyone please help shine some light on the possible cause of my problem as I've run out of ideas?

Offline Hood

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Re: Z Axis loosing steps in the up direction only.
« Reply #1 on: January 24, 2014, 03:15:13 AM »
Reduce your Accel and Vel for the Z by maybe 20% and see if that helps.
Check all your wiring is secure.
If you attach your xml I will have a look through that to see if there is a problem with it.
Hood
Re: Z Axis loosing steps in the up direction only.
« Reply #2 on: January 24, 2014, 03:39:17 AM »
Thanks for your thoughts Hood.
I've played around with Acc and Vel, going from one extreme to another and all points in between with no change.
I have looked at all my wiring terminals and came up empty handed.
There are IDE cables running between the BOB and driver boards. I have changed them all around, but still no change.
I've changed key boards over. No change.
I have the same result when jogging with the Mach3 pendant callout.

I have the hard drive out of the computer at the moment as I'm seeing if I can sustitute it to another PC. I'll post up the XML as soon as I can.

I was going to try fitting a PCI parallel port card to my PC and see if the mother boards port is at fault.
Do you think that would be worth a try? They are pretty cheap and if they work, then that may be a better way to go rather than replacing the mother board.
Unfortunatly we have a public holiday here this weekend, so all the shops will be shut. >:(

Thanks again.
Re: Z Axis loosing steps in the up direction only.
« Reply #3 on: January 25, 2014, 04:43:58 AM »
Ideally you'd want to isolate the fault before tearing down a system and PC, swapping steppers to alternate drivers, drivers to alternate break out board outputs and so on can allow you to identify the common component or connections present on the axis displaying faults.
Trying to solve an unidentified fault using untested parts is a recipe for an extended headache, it might just work first time though ;-)

 - Nick

Offline Tweakie.CNC

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Re: Z Axis loosing steps in the up direction only.
« Reply #4 on: January 25, 2014, 05:16:52 AM »
Quote
I then ran the stepper without it being connected to the ball screw and found that jogging in the down direction the motor runs perfectly, but jogging in the up direction the motor jerks and moans and looses steps. Sometimes it even runs the wrong direction.

Assuming all electrical wiring is indeed correctly connected...
Try selecting Sherline 1/2 Pulse Mode, apply, then do a Mach3 restart and just see if that cures this issue.
If it does not then it could either be the Z axis direction pin is faulty on your LPT parallel port (or BoB) or the Z axis motor driver is faulty. You may be able to swap pin numbers for Z axis direction signal and rule out one possibility.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Z Axis loosing steps in the up direction only.
« Reply #5 on: January 26, 2014, 06:44:41 AM »
Ideally you'd want to isolate the fault before tearing down a system and PC, swapping steppers to alternate drivers, drivers to alternate break out board outputs and so on can allow you to identify the common component or connections present on the axis displaying faults.
Trying to solve an unidentified fault using untested parts is a recipe for an extended headache, it might just work first time though ;-)

 - Nick
I have 4x driver boards and 4 motors in my set up and I've swapped them all around and covered all combinations.
The only board I don't have a spare, is the BOB.
I have narrowed it down as much as I can to either the BOB or a problem with the parallel port.
I have just been given another PC with the correct ports, so I'll try that and see what I get.
Re: Z Axis loosing steps in the up direction only.
« Reply #6 on: January 26, 2014, 06:50:54 AM »
Quote
I then ran the stepper without it being connected to the ball screw and found that jogging in the down direction the motor runs perfectly, but jogging in the up direction the motor jerks and moans and looses steps. Sometimes it even runs the wrong direction.

Assuming all electrical wiring is indeed correctly connected...
Try selecting Sherline 1/2 Pulse Mode, apply, then do a Mach3 restart and just see if that cures this issue.
If it does not then it could either be the Z axis direction pin is faulty on your LPT parallel port (or BoB) or the Z axis motor driver is faulty. You may be able to swap pin numbers for Z axis direction signal and rule out one possibility.

Tweakie.

I didn't think I could swap pin numbers. I have pin #6 for Z step and #7 for Z direction. What pins would I be able to use other than these?
But bear in mind that the machine was running perfectly ok till I told it to drive through the job. Changing pins around seems to be an odd thing to do, but I guess it could help narrow down a possible faulty pin in the parallel port.
Re: Z Axis loosing steps in the up direction only.
« Reply #7 on: January 27, 2014, 05:00:42 AM »
I tried a few more things today with absolutely no change.
Tried Sherline 1/2 pulse. No difference after restart so changed it back.
Played around with pin numbers but couldn't get anything to work.
Here is my XML file if anyone would be so kind to look at it.

Thanks for all the suggestions.
I have a PCI/parallel port card coming and maybe that will solve my issue.
Failing that I'll see if I can get my other comp to work.

Offline Hood

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Re: Z Axis loosing steps in the up direction only.
« Reply #8 on: January 27, 2014, 05:16:04 AM »
That is not the correct  xml as it has no config in it at all.
Hood
Re: Z Axis loosing steps in the up direction only.
« Reply #9 on: January 27, 2014, 05:21:53 AM »
That is not the correct  xml as it has no config in it at all.
Hood

Oh!
I've never had to use that type of file, so I simply looked for a file of that name in my Mach folder. I'll have another look around. If I open the xml file, what should I be able to see?